1. Field of the Invention
The present invention generally pertains to clothes dryers and, more particularly, to clothes dryer moisture sensors.
2. Description of Related Art
As clothes dryers have evolved, it has become common to provide controls to automatically terminate a drying operation. Initially, these controls consisted of user-set mechanical timers. However, mechanical timers are only operable to switch between modes of operation after a predetermined period of time, and may tend to over-dry or under-dry clothes.
An improved system monitors the humidity of the air stream in the exhaust duct and correlates the clothes wetness or moisture content to the sensed humidity. When the sensed humidity corresponds to a user-selected dryness condition, the drying operation is discontinued. Systems utilizing exhaust duct humidity sensors have been on the market for a number of years.
Similarly, it has become common to provide sensors within the clothes receiving compartment which are contacted by the tumbling clothes during a drying operation. Generally, a pair of elongated or bar-shaped sensor electrodes are provided within the dryer and face toward the interior of the dryer drum such that clothes being tumbled and dried will periodically engage and bridge the electrodes. The sensed resistance between the electrodes is used to determine the dryness of the clothes.
A high resistance between the electrodes is indicative of either an open circuit (no clothes bridging with the electrodes) or that the clothes are dry. A low resistance between the electrodes is indicative of wet clothes bridging the electrodes. A short circuit is indicative of a conductive element (button, zipper, etc) bridging the electrodes. Appropriate control circuitry, including time delays, make it possible to determine when the clothes have reached a desired dryness condition. As such, the elongated electrodes may be an essential part of an automatic control system for a clothes dryer. However, the placement and long-term viability of moisture sensors within the dryer drum has been problematic.
One attempt to provide dryness electrodes within a clothes dryer is illustrated by U.S. Pat. No. 4,899,464 to Carr et al. The '464 patent discloses a pair of sensor strips secured to a dryer outlet grill. The outlet grill is secured to a front wall of the dryer cabinet, faces toward the interior of the drum, and covers an exhaust duct that receives exhaust air from the drum. The grill defines a plane which is at an angle to the plane of the front wall. The sensor strips are provided at a lower end of the grill, and are provided near an outer periphery of the drum.
The sensor strips of the '464 patent are mechanically attached to the grill by making use of projections from the strips and cooperating recesses and walls provided by the grill. Unfortunately, since the grill and strips are formed from different materials having different coefficients of thermal expansion, and since the interior of the clothes dryer is subject to repeated heating and cooling, the sensor strips may tend to loosen over time. Moreover, lint tends to accumulate beneath the sensor strips and may tend to push the sensor strips away from the grill. As such, buttons, loops, or other projections from clothing may become snagged on the sensor strips, damaging the strips or the clothes.
Therefore, there exists a need in the art for an improved grill assembly wherein the moisture sensors are permanently affixed to the grill and will not move relative to the grill. There also exists a need in the art for a grill assembly wherein the sensors will not trap lint or become entangled with clothing within the drum. Finally, there exists a need in the art for a grill assembly wherein the air flow passage provided by the grill is maximized, and the provision of sensor electrodes on the grill assembly does not significantly reduce the size, number, or location of the grill openings.